Capacitive discharge ignition circuit using a gate controlled semiconductor switch



Jan. 10, 1967 OIV- OFF 28 H. P. QUINN CAPACITIVE DISCHARGE IGNITION CIRCUIT USIN A GATE CONTROLLED SEMICONDUCTOR SWITCH Filed April 14, 1964 T '1 I11 620550 44 at. Po/N rs Ik I P75. K4475 l E i I 45 6'47: V0475 -4 i -4"; 4; W d iflir/rmfmws i 1 l fiWM/IQ/ V04 rs i 4LAYE1WODE 3/4/50 To/V7204: 0 Fee 72 51? Imam me #44 say P. dam/N M L ama:

CAPACITIVE DISCHARGE IGNITION CIRCUIT USING A GATE CONTROLLED SEMICON- DUCTOR SWITCH Halsey P. Quinn, Morris Plains, N.J., assignor to Tung- Sol Electric Inc., a corporation of Delaware Filed Apr. 14, 1964, Ser. No. 359,638 6 Claims. (Cl. 315-214) This invention relates to an ignition circuit for internal combustion engines using a semiconductor gate controlled switch for turning current on and off through an inductor having a ferromagnetic core. The invention has specific relationship to an ignition circuit which produces high voltage and yet has only a few circuit components.

Many ignition systems for internal combustion engines have been designed and constructed using transistors, diodes, and a variety of inductors and transformers. Most of these circuits are subjected to over-heating and possible failure due to the current carrying limitations of the transistors in the circuit. The present preferred circuit uses no transistors nor any vacuum tubes but instead uses a gate controlled switch having an anode, a cathode, and a control electrode. The switch is constructed so that a positive pulse of one volt (or .1 of an ampere) will turn the gate on and permit current to flow between the anode and cathode. Also, a negative pulse applied to the control electrode of 10 to 15 volts will turn the gate ofi and reduce the current flow to zero.

One of the objects of this invention is to provide an improved ignition circuit for internal combustion engines which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to reduce the cost of dependable ignition circuits.

Another object of the invention is to provide a high voltage pulse having a very fast rise time. This type of voltage pulse can be used on old and leaky spark plugs.

Another object of the invention is to eliminate the high current flow through the breaker points generally required on most ignition circuits.

The invention comprises an ignition system for internal combustion engines having a series of explosive chambers, each with a spark plug. A pair of breaker points are connected in series with the primary of the first transformer and a source of direct current which may be a storage battery. A gate controlled switch and an inductor with a ferromagnetic core are connected in series and bridged across the battery terminals. The gate controlled switch includes a control electrode for turning the switch on and off. The control electrode is connected to the secondary winding of the first transformer which is connected in series with a diode rectifier. A storage capacitor and a second rectifier are connected in series across the anode and cathode of the gate controlled switch and a second or output transformer has its primary winding connected across the rectifier. The secondary winding of the transformer is coupled to the spark plug array in series with the usual distributor.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a schematic diagram of connections of the preferred form of the ignition circuit.

FIG. 2 is a schematic diagram of connections of an alternate form of the circuit.

FIG. 2A is a legend explanatory of the symbols employed for elements of the circuit of FIG. 2.

FIG. 3 is a graph showing some of the current and voltage pulses that occur within the circuit.

hired States Patent 3,297,911 Patented Jan. 10, 1967 Referring now to FIG. 1, the circuit includes a source of direct current potential 10, which may be a storage battery, an on-off switch 11, and the usual pair of breaker points 12 which are opened and closed by a cam 13 secured to a shaft 14 which is coupled to the distributor arm 15. The breaker points 12 are connected in series with the primary winding 16 of a first transformer 17 having a secondary winding 18 and a core 20. A limiting resistor 21 is connected in series with primary winding 16 and the battery 10. A semiconductor gate control switch 22 is the main operating component of the circuit. This switch has an anode 22A, a cathode 22B for the passage of current and a control electrode 22C which triggers the anode and cathode current and permits the passage of considerable current when the switch is closed but reduces the current to zero when the switch is open. The switch is connected in series with an inductor 24 Wound on a ferromagnetic core 25. The induct-or and the anode-cathode circuit of the switch 22 are connected in series with a limiting resistor 26 and this series circuit is bridged across the source of potential 10. The control electrode 22C is connected to one terminal of winding 18 and the other terminal of this winding is connected to a rectifier 27 and the positive terminal of the source of potential. The rectifier 27 is bridged by a resistor 28.

An output transformer 30 includes a secondary winding 31 which is connected to the distributor arm 15 and ground. The distributor includes the usual array of contacts 32 which are connected to the spark plugs 33. The primary winding 34 of the output transformer is connected in series with a storage capacitor 35 and the two are bridged across the anode-cathode circuit of the switch 22. The primary winding 34 is also connected in parallel with a rectifier 36.

The operation of this circuit is as follows: As soon as the on-off switch 11 is closed, the potential of battery 10 acts through resistor 28 and winding 18 to apply a positive potential to control electrode 23 and turn on switch 22. This action permits a current to flow through resistor 26 and inductor winding 24 to create a magnetic flux in core 25. Now, when the engine is started and the breaker points 12 are closed for the first time, current from the battery flows through primary winding 16 of transformer 17 and creates a magnetic flux in core 20. As soon as the points open, the current through winding 16 is cut off and the magnetic field in core 20 collapses and produces a reverse voltage pulse in winding 18 which passes through diode 27 and applies a negative voltage to electrode 22C to turn off switch 22. The duration of this non-conductive condition depends upon the number of turns on winding 18 and other circuit characteristics. It has been found that a non-conducting condition of about micro-seconds produces good results for an internal combustion engine which is operated at speeds normally met within the modern automobile. When gate control switch 22 is turned off, the field in core 25 collapses and a voltage is generated in winding 24 which is transferred to storage capacitor 35 in series with diode rectifier 36. With a 12 volt battery the voltage stored in capacitor 35 is about 440 volts.

As soon as the voltage pulse generated in winding 18 subsides, the normal battery potential of 12 volts is applied to the control electrode 22C and the switch is again turned on permitting the storage capacitor 35 to discharge through the switch and the primary winding 34 of the output transformer 30. This current pulse generates a high voltage in secondary winding 31 and sends a high voltage pulse to one of the spark plugs 33 by way of the distributor arm 15. As soon as the storage capacitor discharges, current again flows from the battery 10 through the inductor winding 24 and the switch 22 to build up a magnetic field in core 25. The rest of the action is a repetition of the action described above.

The set of graphs shown in FIG. 3 provide further information regarding the operation of the circuit shown in FIG. 1. The square-topped pulses 40 indicate the position taken by the points as they open and close. When the points close, a current surge is produced in winding 16 which stores energy in core 20. When the points open, a voltage is produced across the secondary winding 18 having a wave shape similar to waves 41, each having a high initial value. The voltage applied to electrode 23 of the gate controlled switch 22 comprises a first negative pulse 42 when the points open and a much smaller positive pulse 43 when the points close. It will be noted that the normal voltage always applied to this electrode is volts as indicated by line 44. This is due to the fact that electrode 23 is connected through secondary winding 18 and resistor 28 to the positive side of battery 10.

When the gate 22 is actuated, a current flows through the diode 36 and charges the storage capacitor 35, this charge being indicated in FIG. 3 by pulses 45. When this pulse ends, the capacitor 35 discharges through winding 34 in the reverse direction, this pulse being indicated in the graph by pulse 46.

The output pulse generated by secondary winding 31 has the same wave form as pulse 46 but the voltage is stepped up to about 28,000 volts. This is the pulse that is sent to spark plugs 33 by distributor arm 15.

The ignition circuit shown in FIG. 2 has many components which are the same as the circuit shown in FIG. 1. The secondary winding 18 of the first transformer 17 is connected to the trigger electrode of the gate control switch 22 and the anode-cathode circuit of switch 22 is connected in series with an inductance winding 50 on a core 51. However, in the circuit shown in FIG. 2, a secondary winding 52 is provided which is connected in series with a rectifier 53 and the usual storage capacitor 35.

The output circuit of this arrangement includes the distributor arm 15, contacts 32, and spark plugs 33 as before. Also, a secondary winding 31 furnishes the output energy to the distributor and this transformer 30 has a primary winding 34 as shown in FIG. 1. The coupling between storage capacitor 35 and the primary winding 34 is also different than the circuit described above. In FIG. 2, a delay control circuit delays the closing of a silicon controlled rectifier 60 in series with primary winding 34 until the voltage on the storage capacitor has reached a predetermined value.

A resistor 54 and a zener diode 55 are connected in series and bridged across the storage capacitor 35. A second resistor 56 is connected in series with a four layer rectifier 57. The cathode of rectifier 57 is connected to the control electrode 58 of a silicon controlled rectifier 60 which is connected in series between the negative terminal of the battery 10 and the primary winding 34. These two circuit elements are bridged across the storage capacitor 35.

The operation of this portion of the circuit is as follows: as the voltage rises on storage capacitor 35, current also flows through resistors 54 and 56 to charge a second storage capacitor 61. The voltage on resistor 56 is limited by the zener diode 55 so that the charging rate of capacitor 61 is predictable. When the charge on capacitor 61 reaches the breakdown voltage of diode 57, the capacitor is discharged into the control electrode 58 of the sili con controlled rectifier 60 which in turn discharges capacitor 35 through the primary winding 34. This pulse generates the output voltage. The use of a transformer 51 in place of an inductor 24 prevents the gate controlled switch 22 from discharging the storage capacitor 35 if the silicon controlled rectifier is not activated for the passage of current.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. In an ignition system for internal combustion engines which includes a pair of breaker contacts connected in series with a source of direct current and controlled to open and close in synchronism with the movements of the engines pistons; a primary Winding of a first transformer connected in series with the breaker contacts and the source of direct current; an inductor having a winding on a ferromagnetic core; a semi-conductor gate controlled switch having an anode, a cathode, and a control electrode for controlling the resistance of the anode-cathode circuit; said anode-cathode and and said inductor winding connected in series and bridged across the source of direct current; a control circuit for said gate controlled switch connected between the positive terminal of the current source and the control electrode, said control circuit including a secondary winding on the first transformer and a first diode rectifier poled so as to block normal current fiow from the current source; a storage circuit for storing a quantity of electricity generated by the inductor when the magnetic flux in its core collapses; said storage circuit including a storage capacitor and a second diode rectifier connected in series and bridged across the anode-cathode circuit of the gate; and an output transformer including a primary winding and a secondary winding, said primary winding connected across the second diode rectifier in the storage circuit and said secondary winding connected to a distributor.

2. An ignition system as claimed in claim 1 wherein said primary winding of the first transformer is connected in series with a limiting resistor and said secondary winding on the first transformer is connected in series with another resistor which is connected in parallel with the first diode rectifier.

3. An ignition system as claimed in claim 1 wherein said second diode rectifier is connected so as to pass current when the storage capacitor is being charged and to block current when the storage capacitor is being discharged.

4. An ignition system as claimed in claim 1 wherein a secondary winding is added to said inductor to convert it into a transformer, said secondary winding connected to the storage capacitor in series with the diode.

5. An ignition system as claimed in claim 4 wherein a silicon controlled rectifier is connected in series with the primary winding of said output transformer; said silicon controlled rectifier having an anode, a cathode, and a control electrode; and a voltage sensitive control circuit connected across said storage capacitor for applying a control pulse to the cathode and control electrode of the silicon controlled rectifier and thereby permit the storage capacitor to discharge through the primary winding of the output transformer.

6. An ignition system as claimed in claim 5 wherein said voltage sensitive circuit includes a zener diode, a second storage capacitor, and a four layer diode; said four layer diode connected to the control electrode of the silicon controlled rectifier and adapted to conduct only when the voltage across its terminals has reached a predetermined value.

References Cited by the Examiner UNITED STATES PATENTS 3,078,391 2/1963 Bunodiere 315209 3,134,048 5/1964 Wolfi'ram 315-209 3,169,212 2/1965 Walters 315-209 JOHN W. HUCKERT, Primary Examiner.

D. O. KRAFT, I. D. KALLAM, Assistant Examiners. 

1. IN AN IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES WHICH INCLUDES A PAIR OF BREAKER CONTACTS CONNECTED IN SERIES WITH A SOURCE OF DIRECT CURRENT AND CONTROLLED TO OPEN AND CLOSE IN SYNCHROSIM WITH THE MOVEMENTS OF THE ENGINE''S PISTONS; A PRIMARY WINDING OF A FIRST TRANSFORMER CONNECTED IN SERIES WITH THE BREAKER CONTACTS AND THE SOURCE OF DIRECT CURRENT; AN INDUCTOR HAVING A WINDING ON A FERROMAGNETIC CORE; A SEMI-CONDUCTOR GATE CONTROLLED SWITCH HAVING AN ANODE, A CATHODE, AND A CONTROL ELECTRODE FOR CONTROLLING THE RESISTANCE OF THE ANODE-CATHODE CIRCUIT; SAID ANODE-CATHODE AND AND SAID INDUCTOR WINDING CONNECTED IN SERIES AND BRIDGED ACROSS THE SOURCE OF DIRECT CURRENT; A CONTROL CIRCUIT FOR SAID GATE CONTROLLED SWITCH CONNECTED BETWEEN THE POSITIVE TERMINAL OF THE CURRENT SOURCE AND THE CONTROL ELECTRODE, SAID CONTROL CIRCUIT INCLUDING A SECONDARY WINDING ON THE FIRST TRANSFORMER AND A FIRST DIODE RECTIFIER POLED SO AS TO BLOCK NORMAL CURRENT FLOW FROM THE CURRENT SOURCE; A STORAGE CIRCUIT FOR STORING A QUANTITY OF ELECTRICITY GENERATED BY THE INDUCTOR WHEN THE MAGNETIC FLUX IN ITS CORE COLLAPSES; SAID STORAGE CIRCUIT INCLUDING A STORAGE CAPACITOR AND A SECOND DIODE RECTIFIER CONNECTED IN SERIES AND BRIDGED ACROSS THE ANODE-CATHODE CIRCUIT OF THE GATE; AND AN OUTPUT TRANSFORMER INCLUDING A PRIMARY WINDING AND A SECONDARY WINDING, SAID PRIMARY WINDING CONNECTED ACROSS THE SECOND DIODE RECTIFIER IN THE STORAGE CIRCUIT AND SAID SECONDARY WINDING CONNECTED TO A DISTRIBUTOR. 